This invention relates generally to an endoscope, and more particularly to an improved construction of connection between a tip member and a guide tube for guiding a forceps or the like.
Generally, an endoscope comprises a body, an insertion tube extending from the body, and a rigid tip member mounted on a distal end of the insertion tube. That portion of the insertion tube which is close to the tip member and has a predetermined length serves as a bending portion. This bending portion is bent in a remotely-manipulated manner by a manipulation means provided on the body. The endoscope further comprises a flexible guide tube for guiding a forceps and the like. The guide tube is connected at its proximal end to an inlet port in the body, and extends through the body and the insertion tube, and is connected at its distal end to an outlet port in the tip member.
A construction of connection between a tip member and a guide tube is shown in FIG. 3 of Japanese Utility Model Publication No. 3-15042. More specifically, a stepped bore is formed axially through the tip member. A front end portion of this stepped bore serves as an outlet port, and a rear end portion of the stepped bore is greater in diameter than the outlet port. A front end portion of a rigid connection pipe is press-fitted in the rear end portion of the stepped bore, and is fixedly secured thereto by soldering or the like. The rear end portion of this connection pipe is projected from the rear end face of the tip member, and the guide tube is mounted on the outer periphery of this connection pipe in an expanded manner.
In the above connection construction, even if an adhesive is provided between the connection pipe and the guide tube, the connection strength obtained is low. Furthermore, in the above connection construction, the inner diameter of the guide tube is equal to the diameter of the outlet port and the inner diameter of the connection pipe, and is relatively small. When the insertion tube is bent along a body cavity, or is bent by remote manipulation, the corresponding portion of the guide tube is also bent to have an oval cross-sectional shape. If the inner diameter of the guide tube is small, the resistance to the passage of a forceps is increased at that portion of the guide tube having such an oval cross-sectional shape.
An improved construction between a guide tube and a tip member is shown in FIG. 1 of the above Japanese Utility Model Publication No. 3-15042. More specifically, external threads are formed on the outer periphery of the front end portion of the guide tube. On the other hand, internal threads are formed on an inner periphery of a rear end portion of a stepped bore in the tip member. By threading the front end portion of the guide tube into the rear end portion of the stepped bore in the tip member, the guide tube and the tip member are connected together. In this connection construction, a high connection strength is obtained because of the use of the threaded connection. However, since the inner diameter of the guide tube is equal to the inner diameter of the outlet port, and is relatively small, the resistance to the passage of a forceps is increased at the bent portion of the guide tube, as described above. When it is intended to increase the inner diameter of the guide tube, the inner diameter of the rear end portion of the stepped bore must also be increased, and in this connection the diameter of the tip member must also be increased, because the strength of the tip member 1 is lowered if the inner diameter of the stepped bore is increased without increasing the outer diameter of the tip member.